Bathymetric distribution of benthic macroinvertebrates in deep Lake Motosu, Fuji Five Lakes, Japan

Abstract

The distribution of benthic macroinvertebrates was studied in deep Lake Motosu (oligotrophic lake), Japan. Bathymetrical sampling surveys were carried out using a standard Ekman grab at each of 16 stations in the lake on 8 March 2013. The average densities of the benthic community for all the stations were 2185 ind./m2, comprised principally of Tubifex tubifex (Muller) 23.4%, Asellus hilgendorfi Bovallius 4.9% and chironomids 65.8%. T. tubifex and chironomids inhabited the entire lake bottom, with higher densities in the shallower region (25 m>) than in the deeper region (ca. 120 m). On the other hand, the density of A. hilgendorfi increased with water depth and was highest in the deeper regions (>70 m). The densities of chironomid larvae were lower in the deeper region, with fewer chironomid larvae located in the center of the lake (637 ind./m2). The most abundant species, Micropsectra yunoprima Sasa, exhibited the widest distribution from 10.0 m to 121.0 m (mean density 926 ind./m2), followed by Procladius choreusi (Meigen) from 10 m to 74.1 m (mean density 365 ind./m2). The results of this study were compared to previous data by Kitagawa (1973) on chironomid larvae. The densities of these chironomid larvae increased throughout the whole lake in 2013. The water quality has not undergone a major change since the 1970’s. In this study, the number of M. yunoprima larvae has shown a tendency to increase, especially in shallower regions; where they are widely distributed, suggesting the continuation of favorable bottom condition for larvae since the 1970’s.